Size of stock twins vs a single turbo.

Im seeing more and more, generally stateside, people running single turbo set ups on stock fuelling, and while I don't agree with it I have done it myself before I took the Aristo off the road.

My question is though, what would the combined size of the 2 stock compressors and turbines be, to equate it to a single turbo and be able to run it safely on stock fuelling?

I am interested in this, just from the perspective of replacing knackered twins.

not sure of sizing but its going to be crasy small by todays standards , also the stock fueling is still not quite right for a single over the sequencial , that being said the injectors stock are 440cc so would have to be a 450 tops single turbo spec i would expect t3 flange 52mm

Maybe a Borg Warner S360 T4 0.88 undivided turbocharger

Using this kit from Paul as a guidance. http://www.garagewhifbitz.co.uk/toyota/supra/turbo-upgrades/turbo-kits.html/garage-whifbitz-2370.html

something like this i would of thought http://www.precisionturbo.net/turbochargers/aftermarket-replacement/details/Aftermarket-Replacement-Turbocharger---5130/76

problem being alot of fabrication requiered due to the availablity of the T3 manifold for the 2jz gte and bolt patten for down pipe .

you can go bigger and just limit boost but sort of defeats the point i was looking at the 58mm precission turbos for around 500 bhp for an auto single set up ,but that being said my T67 bdd doesnt spool that bad anyway with the smaller turbine housing so not worth it for me until it fails then upgrade to something smaller

Mathematically, the equivalent sizes for a single turbo would be:

JDM spec:

Twins:

Compressor: 37/62

Turbine: 48/60

Equivalent Single:

Compressor 52.3/87.7

Turbine 67.9/84.9

UK Spec:

Twins:

Compressor 39/58

Turbine 44/52

Equivalent Single:

Compressor 55.1/82.0

Turbine 62.2/73.5

Based on the calcs above, a 52mm to 55mm turbo should be fine.

Mathematically, the equivalent sizes for a single turbo would be:

 

JDM spec:

Twins:

Compressor: 37/62

Turbine: 48/60

 

Equivalent Single:

Compressor 52.3/87.7

Turbine 67.9/84.9

 

UK Spec:

Twins:

Compressor 39/58

Turbine 44/52

 

Equivalent Single:

Compressor 55.1/82.0

Turbine 62.2/73.5

 

Based on the calcs above, a 52mm to 55mm turbo should be fine.

Thats funny as the jspec are actually bigger then the uk ? Its just that the uk spec are steal

Maybe a Borg Warner S360 T4 0.88 undivided turbocharger

 

Using this kit from Paul as a guidance. http://www.garagewhifbitz.co.uk/toyota/supra/turbo-upgrades/turbo-kits.html/garage-whifbitz-2370.html

That doesn't run with stock fueling Matt. It needs a piggy-back for extra fueling on the stock injectors to run at just 7psi.

That would be a Turbo of the Garrett GT(X)28 Range or other same size Turbos from other manufacturers. Still ECU upgrade or piggy back are mandatory IMHO.

A 67mm turbo would need to run quite low boost to stay on stock fuelling. BPU++ twins are already in dodgy territory even with higher rated fuel pumps and raised fuel pressure. I'm still convinced that the Do-Luck was running ridiculous fuel pressure through stock pink injectors from Japan which would explain why those injectors were in it and it still performed up to 1.1 bar. Might go a way to explaining the heat damage to the fuel pump wiring and also the damage caused to the fuel pump control electronics in the AEM.

Looks like the answer is 52-55 to leave all as is. The map would still lean out at the turbo switch over point which is often seen when using ETTC

This is something I have pondered on many times. The thing is, now with excellent piggy backs available such as the ecu master DET3 fuelling and timing tweaks can be added to this sort of set up for a very small amount of money. Its an avenue I may well go down if my twins give up.

Mathematically, the equivalent sizes for a single turbo would be:

 

JDM spec:

Twins:

Compressor: 37/62

Turbine: 48/60

 

Equivalent Single:

Compressor 52.3/87.7

Turbine 67.9/84.9

 

UK Spec:

Twins:

Compressor 39/58

Turbine 44/52

 

Equivalent Single:

Compressor 55.1/82.0

Turbine 62.2/73.5

 

Based on the calcs above, a 52mm to 55mm turbo should be fine.

Thanks for that, great answer.

The stock fuelling is never going to be right for the tubby on the stock ECU, but with a bit of mapping a wee GTX30r would do nicely I think. Wouldn't be able to run it much past a bar, if at all, but it would be so much faster at coming on than stock.

See, I don't know why it would be an issue running a small single on the stock map. Its just referencing MAP, throttle, O2 etc to the ECU. Unless the stock map is inherently flawed?

But re running at a bar, thats what the stock boost cut is anyway so no problem surely.

Thats funny as the jspec are actually bigger then the uk ? Its just that the uk spec are steal

A bigger turbine on the Jspec (as they used the lighter ceramic turbine wheel), but they have a smaller compressor, so slightly lower hp capable.

See, I don't know why it would be an issue running a small single on the stock map. Its just referencing MAP, throttle, O2 etc to the ECU. Unless the stock map is inherently flawed?

But re running at a bar, thats what the stock boost cut is anyway so no problem surely.

The stock ECU will probably dump some extra fuel in around 4000rpm as it would think the second turbo is spooling then, but apart from that it should run a small single just fine. No different to people running true-twin with the stock turbos.

See, I don't know why it would be an issue running a small single on the stock map. Its just referencing MAP, throttle, O2 etc to the ECU. Unless the stock map is inherently flawed?

But re running at a bar, thats what the stock boost cut is anyway so no problem surely.

There's a big difference between a modern turbo at 1.0bar and a pair of old twins at 1.0bar though. The density of the 1bar charge will be much higher with a GTX, as an example, so the fuel would need to be added as required across the map.

When the ECU sees 1bar I think it just dumps the fuel so it would run really rich at

As the TTC mod was mentioned previously, that's a good example to use to emphasise my point. The gains from using an aftermarket in TTC mode are far higher than seen from sequential. The reason for this is the TTC mode runs pretty crap without a bit of tweaking, not to the point where it's an issue... but it's far from ideal.

There's a big difference between a modern turbo at 1.0bar and a pair of old twins at 1.0bar though. The density of the 1bar charge will be much higher with a GTX, as an example, so the fuel would need to be added as required across the map.

For those people just wanting a similar performance single (aka 52-55mm range) to replace old twins, then the stock fueling is fine up to 1 bar as the ECU learns very well using the O2 feedback loop for normal driving. E.g. I've run 550cc injectors with the stock JDM ECU and within 20km driving, it has compensated completely for the injector size difference for normal driving. As you go bigger in turbo size, then the differences in efficiencies at boost under 1 bar become greater and you would definitely want to run some form of fuel control adjustment.

When the ECU sees 1bar I think it just dumps the fuel so it would run really rich at

 

The stock ECU only dumps fuel in at around 4000rpm for the second turbo, so at less than 4000rpm it will run fine.

The stock ECU only dumps fuel in at around 4000rpm for the second turbo, so at less than 4000rpm it will run fine.

Are you absolutely sure about that? You seem to be making a lot of assumptions in all of your posts. As I understand it the ECU fuel dumps once it senses over 1.0bar, this just happens to be 4krpm with the stock twins.

I wouldn't even attempt this. The cost for the turbo and trimmings and the cost of replacing the engine should it overfuel like crazy just isn't wort it when you can spend a few extra £100 to get it done right.

Are you absolutely sure about that? You seem to be making a lot of assumptions in all of your posts. As I understand it the ECU fuel dumps once it senses over 1.0bar, this just happens to be 4krpm with the stock twins.

 

I wouldn't even attempt this. The cost for the turbo and trimmings and the cost of replacing the engine should it overfuel like crazy just isn't wort it when you can spend a few extra £100 to get it done right.

On a completely stock setup, max boost is 11 psi (not 1 bar) as fuel cut occurs at just over 1 bar. The fuel dumping you refer to is in relation to the second turbo coming online which usually happens at around 4000rpm.

My comments are not assumptions, but are based on how the sequential system works:

http://www.max-boost.co.uk/max-boost/supra/boosting_the_beast.htm

http://www.max-boost.co.uk/max-boost/supra/turbo.htm

V8kiler is right scott the stock ecu dumps at 4000 rpm , the problem insee with the small single turbo is that the stock ecu trys to keep in closed loop all the way to 0.6 bar throttle position and speed of compression taken into account , and the 0.6 on the small single vs the first small turbo if single is just flowing so much more air it will need fueling to be adjusted in the closed loop area.

Larger single turbos like mine dont have this issue as the main boost build is at the point of the 4k dump and even then i have to pull crazy amount of fuel at this point with my piggy.

I appreciate the air flow thing, which is why I mentioned the CFM thing, a bigger compressor will obviously flow more air for a given boost figure, which is why I said same dimensions as the combined twin turbos. I also appreciate that compressor design has moved on somewhat. So what we're basically saying its entirely possible, but the stock map is a bit wack?

V8kiler is right scott the stock ecu dumps at 4000 rpm , the problem insee with the small single turbo is that the stock ecu trys to keep in closed loop all the way to 0.6 bar throttle position and speed of compression taken into account , and the 0.6 on the small single vs the first small turbo if single is just flowing so much more air it will need fueling to be adjusted in the closed loop area.

Larger single turbos like mine dont have this issue as the main boost build is at the point of the 4k dump and even then i have to pull crazy amount of fuel at this point with my piggy.

I don't think that's right, but I don't have any links to back up what I'm saying. I don't know any car that is mapped to dump at an RPM. That would suggest that the injectors are working at 100% when you rev over 4krpm regardless of load and regardless of MAP sensor pressure, that's just not the way cars work but I'm no mapper so will just agree to disagree. For me, MAP sensor cars set their injector duty based on rpm AND boost pressure rather than just RPM. With regards to the sequential system, it's only BPU that dumps the fuel, that I recall, and it's due to the ECU seeing 1bar of pressure so it does what it can to preserve the engine (dumps fuel). If this happened at 3krpm, it would do the same.

However, if you are indeed all correct then that would mean the car would run silly lean on a decent turbo until 4krpm when it eventually started dumping fuel to meet the turbo's demands.

I appreciate the air flow thing, which is why I mentioned the CFM thing, a bigger compressor will obviously flow more air for a given boost figure, which is why I said same dimensions as the combined twin turbos. I also appreciate that compressor design has moved on somewhat. So what we're basically saying its entirely possible, but the stock map is a bit wack?

Indeed. It wouldn't take much to fix though. A piggyback would do the job fine if a stand alone was too much of a stretch. Everything about the car as it stands is fine physically for such an application, it would just need the control tweaking to work properly.

I don't think that's right, but I don't have any links to back up what I'm saying. I don't know any car that is mapped to dump at an RPM. That would suggest that the injectors are working at 100% when you rev over 4krpm regardless of load and regardless of MAP sensor pressure, that's just not the way cars work but I'm no mapper so will just agree to disagree. For me, MAP sensor cars set their injector duty based on rpm AND boost pressure rather than just RPM. With regards to the sequential system, it's only BPU that dumps the fuel, that I recall, and it's due to the ECU seeing 1bar of pressure so it does what it can to preserve the engine (dumps fuel). If this happened at 3krpm, it would do the same.

Obviously it doesn't just always dump fuel in at 4000 rpm for no reason. My comments were for when the #2 turbo is coming online, which only happens if you are already at significant boost with the #1 turbo.

Yeah it dumps when you are still in the closed loop sub 0.6 as it hits 4000 rpm it just opens up the flood gates, I could simply prove this by doing a video of my afr and boost controler.

It may even do it at wot open loop from the stand still but you just go through the 4000 rpm point to quickly, it only does it 4000-4300 tops

But obviously with the correct sized turbo, its exactly the same a TTC and lots of people run this way with no additional mapping but I would still wantva piggy at least with a afr gauge